Lyocell is a natural cellulosic fiber spun from an amine oxide solvent developed by American ENKA, Asheville, N.C. in the late 1970's. Courtaulds Fibers Inc. of Axis, Ala. ("Courtaulds") markets lyocell fiber under the brand name TENCEL in lengths suitable for short-staple and worsted and woolen spinning systems. TENCEL has a highly crystalline structure and is fabricated from an amine oxide solvent of N-methylmorpholine N-oxide, commonly referred to as NMMO. The industry has found that TENCEL materials are superior to other cellulosics, including cotton and rayon in tensile and aesthetic properties which make it suitable for use in the textile field.
A wide diversity of fabric finishes may be imparted to lyocell fabrics by employing wet processing and enzyme finishing techniques which "fibrillate" the fibers in the fabric. Fibrillation is the formation of micro-fibrils on the surface of fibers as a result of mechanical abrading or splitting of the fiber. It is well known in the textile field that wet processing techniques can be employed to control fibrillation to obtain aesthetic effects.
Courtaulds provides recommended wet processing conditions for finishing TENCEL fabrics. In general, the preferred processing techniques consist of initial wet processing to fibrillate surface fibers in the fabric, an enzyme treatment to remove the surface fibrillation, and a secondary wet processing to fibrillate fibers in the fabric body to provide a "peach skin" or suede fabric finish. Additional recommended processing includes use of scouring techniques, caustic agents and softeners.
Conventional lyocell wet processing techniques have not proven entirely satisfactory because they require long duration washing cycles and controlled enzyme treatments to obtain useful results. It is also found that conventional processing does not consistently yield uniform finishes in lyocell fabrics.
Hydroenhancement techniques have been developed for enhancing the surface finish and texture, durability, and other characteristics of woven or knit spun and spun filament yarn fabric. For example, such techniques are described in commonly owned U.S. Pat. Nos. 4,967,456 and 5,136,761 of H. Sternlieb et al. The hydroenhancing process generally includes exposing one or both surfaces of a fabric to fluid jet treatment, followed by removal of moisture from the fabric and drying. During hydroenhancement, the high pressure water jets impact the spun yarns and cause them to bulk or bloom and the fibers in the yarn to become interentangled. Fabrics produced by this hydraulic treatment process have enhanced surface finish and improved characteristics such as cover, abrasion resistance, drape, stability as well as reduced air permeability, wrinkle recovery, seam slippage and edge fray.
It will be recognized by those skilled in the art that it would be advantageous to provide an hydraulic process for continuous production line finishing of lyocell fabrics. However, it has been the general view in the field that such processing is not suitable for promoting adequate fibrillation in lyocell fabric. For example, Courtaulds, technical manual, Dyeing and Finishing TENCEL Fabrics in Garment Form, states that "open width" fabric processes do not fibrillate TENCEL fabrics.
The present invention resides in the discovery that hydraulic treatment, when optimized with respect to specifications of the fluid curtain and process conditions, unexpectedly produces pre-cursor fabrics suitable for further finishing treatment by wet processing techniques. Advantageously, it is found that hydraulic treatment promotes fibrillation in lyocell fabrics and yields a fibrillated fabric finish after wet process treatment. Hydraulic processing in accordance with the invention also yields improvements in fabric properties.
Accordingly, it is a broad object of the present invention to provide an hydraulic treatment finishing process for lyocell fabrics.
A more specific object of the invention is to provide an hydraulic treatment process which uniformly fibrillates and improves physical properties of lyocell fabrics.
A further object of the invention is to provide an hydraulic production line apparatus which is less complex and improved over the prior art.